The present invention relates to semiconductor fabrication and, more particularly, to a method of treating a workpiece with a plasma and to a processing reactor having a plasma igniter and an inductive coupler.
Integrated circuit "chips" typically are fabricated by subjecting a wafer of silicon or other semiconductive material to various processes which develop the desired circuitry in or on the wafer. Many of these processes simply can be thought of as the patterned coating or removal of materials from the wafer, or the implantation of differing species into the wafer. A multiple number of the desired circuits are typically provided on each wafer, and the wafer is then diced to provide the individual integrated circuit chips. Many of the processes and much of the technology developed for the fabrication of integrated circuitry find other uses, such as to form flat panel displays, etc.
Some of the processes mentioned above require the formation of a plasma of ions for treating one or more semiconductor wafers. Etching of a wafer for cleaning before physical vapor deposition (PVD) on such wafer is such a treatment process. A cleaning plasma typically is formed from a nonreactive gas, that is, a gas that is chemically inert to a wafer. Such gas is introduced into a chamber of the reactor having the wafer(s) to be treated, and ions or other particles are accelerated from the plasma to bombard the wafer surface. The wafers are supported within the chamber on an electrically conductive support to which RF energy is supplied to attract and accelerate the plasma ions to the wafer surface.
A problem associated with plasma treating is that it typically takes a relatively high amount of energy to create a plasma within the reactor chamber. Moreover, a plasma tends to start within a reactor chamber at one location and unevenly spread throughout the gas until it is all ignited. The trend toward increasingly dense integrated circuit geometries has resulted in integrated circuit component and device designs of very small geometry. Such small components and devices are electrically sensitive and quite susceptible to damage. It is therefore important to minimize the characteristics of the electrical parameters, e.g., the power, voltage and current, to which a wafer may be subjected during the fabrication of integrated circuitry.
Efforts have been made in the past to reduce the possibility of damage. For example, in certain PVD systems it is the practice to subject a wafer to precleaning with a low-energy, e.g., 500 w argon plasma. To this end, RF energy has been applied to coils surrounding a chamber for inductive coupling of the same into a gas within the chamber to form the plasma. Attention is directed, for example, to published European patent application 9211017.7 (Publication No. 0 520 519 A1), the subject matter of which is incorporated herein by reference. While the desired low energy RF power is all that is needed to sustain a plasma, it still takes a relatively high amount of energy to create the plasma from the argon or other gas within the chamber.
SUMMARY OF THE INVENTION
The present invention reduces the possibility that integrated circuitry being formed on a workpiece may be damaged by the ignition of a treatment plasma. A separate plasma igniter electrode is provided to apply the electrical power to the gas necessary to create the desired plasma. The plasma, once it is initiated, then is sustained by inductive coupling and the desired plasma treatment takes place. Most desirably, the application of power to the ignition electrode is discontinued once the plasma is created. If the process is plasma etching, power is applied to the support itself to attract ions from the plasma for bombardment of the wafer surface.
It is desirable that the ignition electrode be positioned at a location remote from the location at which the wafer is to be supported. This will reduce the likelihood that the high voltage which must be applied by the electrode to create the plasma will damage the integrated circuitry being formed. It is preferred that the ignition electrode be positioned outside the chamber, i.e., be physically separated from the environment in which the plasma is to be created, and the power required for the creation of the desired plasma be capacitively coupled to the gas.
The invention includes both the method of igniting a plasma separate and apart from inductively sustaining the plasma, and specific apparatus which is particularly designed to conduct the method. Other features and advantages of the invention either will become apparent or will be described in connection with the following, more detailed description of a preferred embodiment of the invention.